1. Field of the Invention
This invention relates to arrangements for securing the roof of a structure against damage caused by high winds, earthquakes, and the like.
2. Background Information
Perhaps the most widely used approach to "hurricane-proofing" a building employs metal "hurricane straps" nailed across points where two structural members meet. In particular, this approach involves placing a metal strap along the top plate across each truss or other roof framing member and nailing the strap in place with ten or more nails. This approach is approved by the building codes in force in the State of Florida at the time this application was written, but it is very expensive both because of the labor involved in driving the great number of nails that need to be used, and because of the time required to fully inspect the work.
Many workers in the field have suggested approaches to increasing the survivability of a building subjected to high winds, the approaches comprising anchoring the roof to the foundation or to anchors firmly set in the ground adjacent the protected structure. Notable among such approaches are the following U.S. patents:
Spoozak et al., in U.S. Pat. No. 5,687,512, teach a tie-down arrangement that anchors the periphery of a roof. Their arrangement involves drilling a hole through each rafter and threading a cable through the holes and thereby around the house. They provide a bracket at each corner or wall end to allow the cable to turn and go in another direction. PA0 Bimberg et al., in U.S. Pat. No. 5,623,788, disclose a tie-down arrangement installable over a finished roof. Their tie-down provides a grid of retainers across the roof--i.e., same of their retainers run parallel to trusses, and some run perpendicular. PA0 Zaffino, in U.S. Pat. No. 5,603,186, discloses a tie-down arrangement that involves anchoring a metal band to the foundation, running the band up along the outside of a wall and across the roof. He shows his strap penetrating the roof, rather than wrapping around the overhang. PA0 Frye, in U.S. Pat. Nos. 5,388,378 and 5,355,640, discloses a roof tie down arrangement having support rods running perpendicular to the trusses. At the end of a wall section each of these rods is connected to an eye-bolt screwed into a truss, an arrangement not known to be particularly good at resisting horizontal forces directed along the rod. Frye's approach is also unusual in the large number of potentially leaky roof penetrations employed. PA0 Thesingh, in U.S. Pat. No. 4,078,353, teaches an overall approach to building a house. His approach includes, as one of its features, a tie-down arrangement similar to Zaffino's in having a flexible tensile member that penetrates the roof at the outer edge of a wall. PA0 Lozier et al. (U.S. Pat. No. 5,537,786) show a tie-down system of straps run across an already-installed roof. Their approach includes several intermediate retainers (e.g., one at the ridgepole) to hold each of a plurality of the straps in a respective predetermined position and to prevent damage to parts of the roof. PA0 Lung et al., in U.S. Pat. No. 5,570,549, who propose the use of special clamps in an otherwise conventional top plate tie down arrangement. These clamps allow Lung et al. to replace the commonly used threaded rods with more widely available and less expensive structural reinforcing rods of the type commonly referred to as "rebar". PA0 Schuyler, in U.S. Pat. No. 5,535,561, teaches the use of a spring in an otherwise conventional top plate tie down arrangement. Schuyler's spring holds tension on the tie down rod in the event that the wall timbers shrink. PA0 Ramirez, in U.S. Pat. No. 5,531,054, teaches the use of tie down rods that are not threaded for their full length. He also teaches an embodiment using a bracket at the top of a tie down rod to clamp a single roof framing member to the top plate. In order for Ramirez's arrangement to clamp all of the roof framing members to the top plate, one tie rod would be required for each such truss or other roof framing member. PA0 Coxum, in U.S. Pat. No. 5,491,935, teaches the use of a special reinforcing bar extending about and cast into the perimeter of a foundation slab and having a first plurality of tee-shaped connectors disposed therealong, each of the first plurality of tee-shaped connectors located immediately beneath a corresponding one of a second plurality of tee-shaped connectors attached to a pipe running above the top plate and passing through each of the rafters of a roof. A vertical tensile connection, comprising threaded pipe and an adjusting coupling, runs between corresponding ones of the first and second plurality of tee-shaped connectors so as to draw the top plate and the rafters downwards towards the foundation. PA0 Phillips, in U.S. Pat. No. 5,384,993, teaches the use of sheet metal brackets disposed over pairs of adjacent trusses to connect those trusses to the top plate. Philips teaches anchoring the top plate to the ground by means of a rod running down through the wall to an anchor buried in the ground beneath the protected building, rather than being set into a foundation.
It is also known to reinforce a building wall to resist wind and earthquake damage by the use of what will hereinafter be called a "top plate tie down" arrangement in which a vertically disposed elongate fastening member that can be loaded in tension (e.g., a threaded metal rod) connects a top plate of the protected wall to an anchor disposed beneath the wall. An exemplar arrangement of this sort is made by the Go-Bolt Company of DeLand, Fla. The Go-Bolt apparatus comprises an anchor portion set in position prior to pouring concrete around it, one or more threaded rods interconnected end-to-end so as to reach from the anchor portion to the top frame rail or top plate on a wood-framed wall, and a washer and nut above the top plate so that tightening the topmost nut clamps the top plate rail to the foundation--i.e., an arrangement in which the threaded rod is in tension and the wall studs adjacent the threaded rod are in compression. The basic top plate tie down arrangement for anchoring a wall is compatible with the separate use of hurricane straps, but it does not necessarily provide means for anchoring a truss or other roof framing member disposed above and supported by the top plate. Improvements to the basic top plate tie down arrangement have been taught in a variety of references, some of which describe arrangements for securing trusses to the top plate as well as means of tying the top plate to a foundation or to some other anchor point. Some of the U.S. patents providing teaching in these areas are those of: